How to decribe all bounded Borel functions where Lebesgue integral is zero

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I'm working on an exercise and I'm not quite sure how to answer it. I need to describe all bounded borel measurable functions $f: [0,1] \to [-1,1]$ where $$ \int_{[a,b)} f d\lambda = 0 $$ There is a hint: decomposition $f=f_+ + f_-$ . Here I'm thinking that this means that $f_+ = f_-$ , but I dont know if this is allowed in this setting. My question is how do I solve an exercise like this?